APPLICATION OF DIFFERENT PHYTOPLANKTON QUANTIFICATION TECHNIQUES IN FRESHWATER ECOSYSTEMS

From 1996 to 2000 (2 week intervals), phytoplankton samples were collected from the eutrophic, shallow backwater „Alte Donau“, situated within the city of Vienna (Austria). Phytoplankton quantification was done both with the inverted microscope technique (IMT) and with photosynthetic marker pigments. Estimation of pigment-based algal composition was conducted with CHEMTAX and fixed ratios (pigment per chl-a).
CHEMTAX calculations were done on basis chl-a and biovolume, the results showed almost no difference (e.g. for diatoms r2 = 0.998, n = 175). A high relation was also found between CHEMTAX and fixed ratios (for diatoms r2 = 0.882, n = 175). Correlations between IMT and pigment quantification were generally found to be lower (diatoms r2 = 0.689, greens r2 = 0.243). Beside the physiological stage of algae, these discrepancies could be explained mainly by the IMT, the results of which are highly influenced by the person responsible for cell counting.